1. Field of the Invention
The present invention relates to a motor driven valve and a controller therefor.
2. Description of the Related Art
A refrigeration cycle in an automotive air conditioner generally includes a compressor for compressing circulating refrigerant, a condenser for condensing the compressed refrigerant, an expansion valve for throttling and expanding the condensed liquid refrigerant and delivering the resulting spray of gas-liquid mixture refrigerant, and an evaporator for evaporating the misty refrigerant and cooling the air in a vehicle interior by evaporative latent heat. For the expansion valves, mechanical expansion valves have been widely used. Such a mechanical expansion valve senses the temperature and the pressure of refrigerant at an outlet side of the evaporator and autonomously opens and closes a valve section thereof. Alternatively, motor operated expansion valves have also been increasingly used with the recent widespread use of electric vehicles and hybrid vehicles. Motor operated expansion valves achieve accurate control of the valve opening degree by means of stepping motors as drive units.
Such a motor operated expansion valve includes a needle-like valve element, for example, for opening and closing a valve hole of a small diameter formed in a body thereof, and a motion converting mechanism configured to convert rotational movement of a rotor into translational movement of a shaft to drive the valve element (refer to Japanese Patent Application Publication No. 2014-196810, for example). The valve element is supported by an end of the shaft, and opens and closes a valve section by leaving and touching a valve seat formed at an open end of the valve hole. In order to achieve high valve element seating characteristics, some motor operated expansion valves have such a structure in which a valve element is elastically supported by a shaft and pressed against a valve seat by the elastic force so that a valve closed state is maintained.
The valve opening degree of such a motor operated valve is controlled by setting of driving steps relative to a valve switching point (a switching position between opening and closing of a valve section). The valve switching point, however, may vary from one valve to another depending on differences in size of components of the valves, assembly errors between components, or the like. Furthermore, after initiation of use (after the first use) of a motor operated valve, the valve switching point may change owing to use environment such as the influence of vibration. The valve switching point thus needs to be set in view of the differences and the change in the valve switching point due to such factors.
In view of the above, a motor operated valve in which a valve opening point is detected every preset time after staring use of the motor operated valve is proposed (refer to Japanese Patent Application Publication No. 2012-149857, for example). Specifically, the motor operated valve is opened by a predetermined opening degree every predetermined time from the fully closed position, and the valve opening degree when the temperature at an outlet of the motor operated valve has changed by a predetermined value or larger is detected to be a valve opening point (lower limit opening degree).